/*
Package transport contains the network transport definitions for rs2322tcp.

This file defines the control protocol messages. It deliberately does not
contain any network I/O. The actual TCP implementation will be added later.

Project: rs2322tcp
Module:  git.lang-dieter.de/rs2322tcp
*/
package transport

import (
	"encoding/json"
	"fmt"

	"git.lang-dieter.de/rs2322tcp/internal/config"
)

///////////////////////////////////////////////////////////////////////////////
// Protocol
///////////////////////////////////////////////////////////////////////////////

// ProtocolVersion is the current control protocol version.
const ProtocolVersion = 1

// MessageType identifies a control protocol message.
type MessageType string

const (
	MessageHello         MessageType = "hello"
	MessageHelloResponse MessageType = "hello_response"
	MessageGetDevices    MessageType = "get_devices"
	MessageDeviceList    MessageType = "device_list"
	MessageError         MessageType = "error"
)

///////////////////////////////////////////////////////////////////////////////
// Generic message
///////////////////////////////////////////////////////////////////////////////

// Message is the common envelope for all control protocol messages.
type Message struct {
	Version int         `json:"version"`
	Type    MessageType `json:"type"`
}

///////////////////////////////////////////////////////////////////////////////
// Hello
///////////////////////////////////////////////////////////////////////////////

// HelloMessage starts a control session.
type HelloMessage struct {
	Message
}

// HelloResponseMessage confirms that the server accepts the protocol
// version used by the client.
type HelloResponseMessage struct {
	Message
}

///////////////////////////////////////////////////////////////////////////////
// Get devices
///////////////////////////////////////////////////////////////////////////////

// GetDevicesMessage requests the devices currently available from the
// server.
type GetDevicesMessage struct {
	Message
}

///////////////////////////////////////////////////////////////////////////////
// Device list
///////////////////////////////////////////////////////////////////////////////

// RemoteDeviceInfo describes a device returned by the server.
//
// DataPort is runtime information belonging to the current server session.
// It is therefore deliberately not part of config.RemoteDevice.
type RemoteDeviceInfo struct {
	ID       string `json:"id"`
	Name     string `json:"name"`
	BaudRate int    `json:"baud_rate"`
	DataBits int    `json:"data_bits"`
	Parity   string `json:"parity"`
	StopBits int    `json:"stop_bits"`
	DataPort int    `json:"data_port"`
}

// DeviceListMessage contains the devices currently available from the
// server and their session-specific data ports.
type DeviceListMessage struct {
	Message
	Devices []RemoteDeviceInfo `json:"devices"`
}

///////////////////////////////////////////////////////////////////////////////
// Error
///////////////////////////////////////////////////////////////////////////////

// ErrorCode identifies a protocol error.
type ErrorCode string

const (
	ErrorUnknownMessage     ErrorCode = "unknown_message"
	ErrorUnsupportedVersion ErrorCode = "unsupported_version"
	ErrorDeviceNotFound     ErrorCode = "device_not_found"
	ErrorDeviceUnavailable  ErrorCode = "device_unavailable"
	ErrorInternal           ErrorCode = "internal_error"
)

// ErrorMessage reports a control protocol error.
type ErrorMessage struct {
	Message
	Code        ErrorCode `json:"code"`
	MessageText string    `json:"message"`
}

///////////////////////////////////////////////////////////////////////////////
// Constructors
///////////////////////////////////////////////////////////////////////////////

// NewHello creates a hello message.
func NewHello() HelloMessage {
	return HelloMessage{
		Message: Message{
			Version: ProtocolVersion,
			Type:    MessageHello,
		},
	}
}

// NewHelloResponse creates a hello response message.
func NewHelloResponse() HelloResponseMessage {
	return HelloResponseMessage{
		Message: Message{
			Version: ProtocolVersion,
			Type:    MessageHelloResponse,
		},
	}
}

// NewGetDevices creates a get-devices message.
func NewGetDevices() GetDevicesMessage {
	return GetDevicesMessage{
		Message: Message{
			Version: ProtocolVersion,
			Type:    MessageGetDevices,
		},
	}
}

// NewDeviceList creates a device-list message from a list of remote
// devices and their session-specific data ports.
func NewDeviceList(devices []RemoteDeviceInfo) DeviceListMessage {
	return DeviceListMessage{
		Message: Message{
			Version: ProtocolVersion,
			Type:    MessageDeviceList,
		},
		Devices: devices,
	}
}

// NewError creates an error message.
func NewError(code ErrorCode, message string) ErrorMessage {
	return ErrorMessage{
		Message: Message{
			Version: ProtocolVersion,
			Type:    MessageError,
		},
		Code:        code,
		MessageText: message,
	}
}

// NewRemoteDeviceInfo converts a public configuration device description
// into the transport representation and adds the session-specific data port.
func NewRemoteDeviceInfo(device config.RemoteDevice, dataPort int) RemoteDeviceInfo {
	return RemoteDeviceInfo{
		ID:       device.ID,
		Name:     device.Name,
		BaudRate: device.BaudRate,
		DataBits: device.DataBits,
		Parity:   device.Parity,
		StopBits: device.StopBits,
		DataPort: dataPort,
	}
}

///////////////////////////////////////////////////////////////////////////////
// JSON
///////////////////////////////////////////////////////////////////////////////

// EncodeMessage encodes a control message as JSON.
func EncodeMessage(message interface{}) ([]byte, error) {
	if message == nil {
		return nil, fmt.Errorf("message is nil")
	}

	return json.Marshal(message)
}